Height adjusting mechanism

ABSTRACT

The height-adjusting mechanism includes a threaded spindle rotatably mounted in a chair base, a nut threaded on the spindle and a seat-supporting column telescopically mounted in the base and carried on a detent washer which in turn rests on top of the nut. A pin projecting from the nut and through elongated vertical slots at the base of the column allows vertical movement of the column with respect to the nut, but fixes the column against rotatable motion with respect to the nut. The detent washer includes a key projecting into a slot in the spindle and includes downwardly projecting detents engaging depressions in the top of the nut and normally preventing rotation of the washer and spindle with respect to the nut. A locking button at the base of the spindle can be depressed upwardly to hold the spindle against rotation such that when the chair is rotated, the column and the nut will rotate with respect to the detent washer and with respect to the threaded spindle and will thereby adjust upwardly or downwardly.

United States Patent [191 Wolters [4 1 Mar. 26, 1974 HEIGHT ADJUSTING MECHANISM Richard H. Wolters, Grand Rapids, Mich.

[73] Assignee: Steelcase lnc., Grand Rapids, Mich.

[22] Filed: Aug. 31, 1972 [21] Appl. No.: 285,188

[75] Inventor:

[52] US. Cl. 248/406 [51] Int. Cl. F16m 13/00 [58] Field of Search..... 248/406, 405, 354 S, 188.4, 248/162; 74/84.15, 424.8; 108/147, 141;

[56] References Cited UNITED STATES PATENTS 457,774 8/1891 Gilson 248/406 1,160,108 11/1915 Hasty 248/406 2,060.075 ll/l936 Herold 248/406 2,504,018 4/1950 Gibson et al.. 74/424 R 2,543,924 3/1951 Mondy 248/406 2,771,787 ll/l956 Dixon 74/424 R 3,386,697 6/1968 Helms 248/406 3,391,893 7/1968 Doerner 248/405 3,606,234 9/1971 Prescott..... 248/406 3,691,858 9/1972 Wilke 74/89.15

FOREIGN PATENTS OR APPLICATIONS 1,226,763 3/1971 Great Britain 248/162 so en Primary Examiner-Marion Parsons, Jr. Attorney, Agent, or Firm-Price, Heneveld, Huizenga & Cooper [57] ABSTRACT The height-adjusting mechanism includes a threaded spindle rotatably mounted in a chair base, a nut threaded on the spindle and a seat-supporting column telescopically mounted in the base and carried on a detent washer which in turn rests on top of the nut. A pin projecting from the nut and through elongated vertical slots at the base of the column allows vertical movement of the column with respect to the nut, but fixes the column against rotatable motion withrespect to the nut. The detent washer includes a key projecting into a slot in the spindle and includes downwardly projecting detents engaging depressions in the top of the nut and normally preventing rotation of the washer and spindle with respect to the nut. A locking button at the base of the spindle can be depressed upwardly to hold the spindle against rotation such that when the chair is rotated, the column and the nut will rotate with respect to the detent washer and with respect to the threaded spindle and will thereby adjust upwardly or downwardly.

11 Claims, 11 Drawing; Figures PATENTED MAR26 I974 SHEET 1 BF 3 PATENTED MARZB I974 SHEET 2 [IF 3 FIG. 5

PATENTEDMARZB I974 3; 799x185 SHEETBUFS liiii i I I :31

FIG. 0 FIG. I l

CROSS-REFERENCE This application is related to patent application Ser. No. 285,527, filed on Aug. 31, 1972, by Robert G. Mohr and Adrian R. Olree. The present invention relates to a means for normally causing a chair supporting column to rotate in conjunction with a threaded spindle with a locking means being provided for locking the spindle against rotation with respect to the chair base whereby the chair supporting column can be rotatably threaded on the spindle. The specific locking means disclosed herein, but not claimed in this application, is the invention of Robert G. Mohr and Adrian R. Olree and is claimed in the aforesaid patent application Ser. No. 285,527.

BACKGROUND OF THE INVENTION The present invention relates to height-adjusting mechanisms for chairs. Normally, a bell nut is rotatably mounted on the chair base and a threaded spindle is threaded in the nut. The chair is mounted at the top of the spindle. Normally, the spindle and bell nut rotate together, generally because of some type of biased detent means therebetween. The height of the chair is adjusted by holding the bell nut and turning the chair to thereby thread the spindle upwardly or downwardly. One drawback to such a mechanism is that the spindle is exposed, at least above the bell nut. The spindle is unsightly and any grease or lubrication thereon becomes exposed to dust. Yet another drawback is that such devices are somewhat mechanically unsophisticated. Patent application Ser. No. 68,178, filed Aug. 31, 1970, by Bernard J. Fries and assigned to the assignee ofthe present application discloses a telescoping chair base in which the threads of the spindle are continually hidden from view by a cover tube which is slidably interconnected to the nut within which the threaded spindle is threaded. One adjusts the height by grasping the cover tube and then rotating the chair. While this mechanism is extremely desirable, it is not optimumly acceptable in all applications.

One prior art mechanism employs a spindle rotatably mounted in the chair base, the chair itself being mounted on a column which is in turn threaded onto the spindle. The bottom of the sheet metal tubular column is actually formed into the shape of a nut having downwardly deviating detents. These detents normally engage indentations in the threads of the spindle such that the column and spindle tend to rotate in unison. When the spindle is locked against rotation with respect to the base by means ofa push plate at the bottom of the base, the detents turn out of the indentations in the spindle threads and the column threads on the spindle. While this mechanism is more sophisticated mechanically, in that one merely pushes a button in order to achieve height adjustment while rotating the chair, it does suffer the drawback in that the formed nut at the base of the tubular column is more readily subject to bending than would be a conventional nut. Such bending may tend to foul the height-adjusting action.

SUMMARY OF THE INVENTION In the present invention, a detent means slidably engages a threaded spindle rotatably mounted in the chair base, the detent means being fixed against rotation with respect to the spindle. This detent means engages a nut which is threadably mounted on the spindle and normally holds the nut against rotation with respect to the spindle. The chair-supporting column is operably connected to the nut such that when the chair and column rotate, the nut, detent means, and spindle also rotate,

all in unison. However, means are provided for locking the spindle against rotation with respect to the chair base whereby when the chair is rotated, the nut disengages the detent means and thereby threads on the spindle. The mechanism is reliable, mechanically sophisticated and can be made of sturdy components.

Preferably, the detent means comprises a washer having at least one downwardly protruding detent engaging a receiving depression in the top of the nut. The column itself is rotatably mounted directly on the washer, and is vertically slidably connected to the nut, but is fixed against rotation with respect thereto. In this manner, when the rotated column turns the nut and forces the detents up out of the depressions in the top surface of the nut, the column is free to slide upwardly with respect to the nut, but continues to be fixed against rotation with respect thereto.

These and other objects and advantages of the invention will be more fully understood and appreciated by reference to the written specification and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a generally cross sectional view of a chair base embodying the height-adjusting mechanism of the invention;

FIG. 2 is a cross-sectional view of the same chair base wherein the chair has been adjusted upwardly;

FIG. 3 is a bottom plan view of the detent washer which rests on top of the adjusting nut and upon which the chair-supporting column rests;

FIG. 4 is a generally elevated perspective view of the height-adjusting nut;

FIG. 5 is a side elevational view of the spindle;

FIG. 6 is a generally perspective view of the cylindri cal sleeve of the chair-supporting column;

FIG. 7 is a generally perspective view of the collar which is secured to the inside of the sleeve of the chairsupporting column;

FIG. 8 is a perspective view of the locking button which is used to lock the spindle against rotation with respect to the base;

FIG. 9 is a generally perspective, cut-away view of the mechanism at the base of the chair-supporting column;

FIG. 10 is a cross-sectional view showing the spindle locking means at the base of the chair base; and

FIG. 11 is the same view as FIG. 10, with the chairsupporting column having been adjusted downwardly to its lowermost point.

PREFERRED EMBODIMENT In the preferred embodiment, spindle 10 is rotatably mounted in chair base 20 (FIG. 1). Nut 30 is threadably mounted on spindle 10. Chair-supporting column 40 is telescopically received within base 20 and rests on a detent washer 50 which in turn rests on nut 30. Column 40 is operably connected to nut 30, being movable vertically with respect thereto, but being fixed against rotation with respect thereto. Detent washer 50 is operably connected to spindle 10, being vertically slidable with respect thereto, but being fixed against rotation with respect thereto. Spindle lock 60 at the bottom of base 20 can be used to lock spindle 10 against rotation with respect to base 20 whereby rotation of chairsupport column 40 will cause nut 30 to rotatably disengage detent washer 50 and thread on spindle 10 either upwardly or downwardly (compare FIGS. 1 and 2).

Spindle 10 comprises a steel shaft or the like having threads 11 thereon (FIGS. and 9). An annular shoulder plate 13 is secured to spindle near the base thereof. Shoulder l3 and a stem 14 projecting downwardly from annular shoulder 13 facilitate rotatable mounting of spindle 10 within base 20. Annular shoulder plate 13 includes a plurality of slots or notches 16 about its perimeter which facilitate the cooperation of shoulder plate 13 with spindle lock 60 to hold spindle 10 against rotation with respect to base 20 (FIGS. 10 and l 1 Spindle 10 includes a groove 12 extending vertically therein from generally its top to its bottom (FIG. 5) for cooperating with detent washer 50 to facilitate the slidable but nonrotatable mounting to spindle 10. Groove 12 is deeper than threads 11 such that a key tab received in groove 12 cannot slip-out between threads 11.

Base 20 includes a hub 21 with outwardly radiating legs 22 (FIG. 1). Hub 21 is generally cylindrical, being hollowed out in the center from its top almost to its bottom for receiving spindle 10 and chair-supporting column 40. The bottom wall 23 of of hub 21 includes an opening 25 therein through which stem 14 of spindle 10 passes. A pair of spindle bearing washers 24 are positioned between bottom wall 23 and shoulder plate 13 to provide a ratatable bearing means at the base of spindle 10. A pair of openings 26 positioned on opposite sides of bottom wall 23 facilitate cooperation of spindle lock 60 with spindle 10 (FIGS. 10 and 11).

Stem 14 of spindle 10 passes through bottom wall 23 and into a downwardly opening cavity 17 in the bottom of base 20. Spindle lock 60 is located generally within cavity 17. To prevent upward removal of spindle 10, a snap ring slips into a receiving groove at the base of stem 14 to lock spindle 10 in place.

A bearing sleeve 27 is inserted in hub 21 in snugly fitting relationship thereto. Bearing sleeve 27 is a selflubricating bearing sleeve made of nylon or the like which extends generally the length of hub 21.

Nut 30, which is threadably mounted on threads 11 of spindle 10 includes depressions 31 in the top surface thereof for cooperating with detent washer 50 (FIG. 4).

In each side of nut 30 there is a pin hole 32 for receiving a pin 33 (FIGS. 4 and 1). Pins 33 facilitate operable connection of nut 30 to chair-supporting column 40 whereby column 40 is free to move vertically with respect to nut 30, but is fixed against rotation with respect thereto. Each pin 33 comprises a swage pin, a screw or other similar fastener.

Column 40 comprises a metal sleeve 41 rigidly joined to a collar 42 at the bottom thereof by means of weld ing or the like (FIGS. 1, 6, and 7). It is telescopically received within bearing sleeve 27 and hub 21. Collar 42 includes a central opening 43 therein through which spindle 10 passes. Sleeve 41 and collar 42 include matching apertures 44 and 45 respectively in the side walls thereof. Apertures 44 and 45 are either elongated in a generally vertical direction (as shown) or are oversized round holes which give the same degree of vertical play for pins 33 as would an elongated slot. They are positioned on opposite sides of column 40 in alignment with pin holes 32 in nut 30. It is through mating apertures 44 and 45 that each pin 33 passes (FIG. 1). In this manner, column 40 is locked against rotation with respect to nut 30, but is free to slide vertically a short distance with respect thereto due to the fact that the apertures have a greater diameter at least in a vertical direction than do pins 33.

Mounted atop column 40 is a chair support 48 which may be of any conventional construction. It is secured to the top of column 40 by means of welding, bolting, or the like.

Collar 42 of column 40 rests directly atop detent washer 50 (FIG. 1). Detent washer 50 in turn rests atop nut 30. Preferably, detent washer 50 is made of metal, but it could be made of a self-lubricating material such as nylon or the like. It includes a key 51 projecting inwardly towards the center thereof for mating engagement with groove 12 of spindle 10 (FIGS. 3 and 9). This fixes detent washer 50 against rotation with respect to spindle 10.

Projecting downwardly from the bottom surface of detent washer 50 are a plurality of detents 52, one for each depression 31 in the top surface of nut 30 (FIGS. 3 and 9). Detents 52 are received within depressions 31 and normally prevent nut 30 from rotating with respect to washer 50 and spindle 10.

Spindle lock 60 for locking spindle 10 against movement with respect to base 20 includes a button 61 formed of sheet metal or the like (FIG. 8). Button 61 includes a pair of upwardly projecting detent fingers 62 (FIGS. 1, 8, l0, and 11). By pushing button 61 upwardly, one can move the upper portion of each detent finger 62 into slot 16 in shoulder plate 13 of spindle 10 (FIG. 10). Each detent finger 62 is wider at its bottom portion than at its top portion and juts inwardly at the base of its top portion to define a limit shoulder 63. Only the upper portion of detent finger 62 is sufficiently narrow to pass through a slot 16, and accordingly, limit shoulder 63 engages the bottom of shoulder plate 13 to prevent further upward movement of button 61.

A guide pin 68 projects upwardly from button 61 and is slidably received in a guide tunnel 69 in stem 14 of spindle 10. The cooperation of guide pin 68 and guide tunnel 69 serves to guide button 61 as it is pushed in or out, thereby minimizing jamming.

The top edge of each detent finger 62 is cut off at an angle on one side to define a sloping wedge 64. The bottom of column 40 acts as an abutment means and is aligned with the top of finger 62. As column 40 is adjusted downwardly within hub 21, its bottom surface abuts the very top of each detent finger 62 and forces detent finger 62 downwardly until wedge 64 is aligned with the edge of receiving slot 16 (FIG. 11). At this point, further rotation of a chair and of column 40 causes the edge of receiving slot 16 to engage wedge 64 and, acting as a cam, actually forces button 61 downwardly against the pressure of a person who is depressing button 61 upwardly. In this manner, detent fingers 62 are forced out of engagement with slots 16 and further downward adjustment of column 40 is prevented. This feature prevents a person from carelessly adjusting column 40 downwardly to the point where it jams against shoulder plate 13 and possibly causes damage to the mechanism.

On the other hand, rotation of the chair and column 40 in an elevating direction will effect upward threading of column 40 even from its lowermost position. This is because wedge 64 is unidirectional, the left side of finger 62 (as viewed in FIGS. and 11) being left vertical, i.e., with a blocking configuration, rather than being cut at an angle at the top. Thus, the left side of notch 16 (as viewed in FIGS. 10 and 11) will engage only the vertical edge of detent finger 62, rather than a sloped wedge surface, and spindle 10 will thereby be prevented from rotation. It is significant that the tip of detent finger 62 can never be forced entirely out of notch 62 by column 40 (although it can be by the cam action of shoulder plate 13). One can always effect upward adjustment of column 40, even from its lowermost position.

A spring 65 mounted between button 61 and the bottom of bottom wall 23 normally biases button 61 downwardly (FIGS. 1, 10, and 11). Thus, detent fingers 62 are normally biased out of engagement with slots 16. A small retainer ring 66 is force fitted or otherwise secured to the very bottom of base at the edge of cavity 17. Its inside diameter is less than the outside diameter of button 61 so that button 61 is prevented from falling out of the bottom of base 20.

Assembly is effected by threading nut 30 onto spindle 10 from the top. Detent washer S0 is then slipped onto spindle 10 with key 51 in groove 12. Spindle 10 is then inserted upwardly through opening 43 in collar 42 of column 40. The apertures 44 and 45 in the base of column 40 are aligned with pin holes 32 in nut 30. Pins 33 are then inserted through apertures 44 and 45 into pin holes 32 and are secured either by a forced fit or, in the case of screws, by threading. Finally, washer 18 is secured to the top of spindle 10 by screw 19 in order to prevent the accidental removal of column 40 from spindle 10.

The assembled column 40, nut 30, detent washer 50, and spindle 10 are then inserted into hub 21 and bearing sleeve 27. Stem 14 is passed through stern opening in bottom wall 23 until shoulder plate 13 comes to rest on spindle bearing washers 24 at the bottom of hub 21.

Spindle lock 60 is assembled to base 20 by positioning spring 65 within locking button 61 and inserting fingers 62 upwardly through opening 26 in bottom wall 23 of hub 21. Retainer ring 66 is then secured to the bottom edge of cavity 17 to hold locking button 61 in place.

In operation, rotation of a chair mounted to chair support 48 rotates column 40 which in turn rotates nut 30. The rotation of nut normally rotates detent washer 50 because of the engagement of detents 52 with depressions 31. Rotation of detent washer 50 results in the rotation of spindle 10 due to the engagement of key 51 with groove 12. Thus, rotation of the chair normally results in simultaneous rotation of column 40, nut 30, detent washer 50, and spindle 10. To adjust the height, the user depresses button 61 upwardly so that the upper portions of detent fingers 62 engage slots 16 in shoulder plate 13 of spindle 10. This holds spindle 10 against rotation with respect to base 20. Detent washer 50 is similarly held against rotation since it is locked against rotation with respect to spindle 10. The user then rotates the chair, thereby rotating column 40 and nut 30. The rotation of nut 30 causes detents 52 to ride up out of depressions 31. The entire column 40 is thereby forced to move upwardly in a vertical direction, but is free to do so because apertures 44 and 45 through which pins 33 project allow vertical movement. Since spindle 10 is fixed against rotation, nut 30 threads upwardly or downwardly thereon to thereby adjust the height. FIG. 1 shows the mechanism in its lowermost position and FIG. 2 shows the mechanism in its uppermost position.

If the chair isbeing adjusted downwardly, column 40 will eventually engage the top of detent fingers 62 (FIG. 11). As column 40 continues to move downwardly, it will force fingers 62 downwardly, in spite of the upward pressure of the user on button 61, until wedge 64 on each detent finger 62 is in line with ,the edge of slot 16 which acts as a cam. At this point, shoulder plate 13 will begin to turn, sliding upwardly along wedge 64. The mere fact that button 61 begins to be pushed in a downward position advises the user that he has reached the bottom. In any event, the slope of wedge 64 is sufficiently gradual that it tends to be overcome by the detent force of detent washer on nut 30. Thus, rotation of column 40 again begins to rotate spindle 10 and shoulder plate 13 actually slides along wedge 64 and over the top of finger 62. This prevents further downward adjustment of column 40 altogether and thereby prevents column 40 from being jammed downwardly against shoulder plate 13.

On the other hand, column 40 can always be adjusted upwardly from its lowermost position since at least the tips of detent fingers 62 can be inserted into notches 16 even with column 40 in its lowermost position and since fingers 62 act as a positive stop against shoulder plate 13 when the chair is rotated in a raising direction.

Of course, it is understood that the above is merely a preferred embodiment of the invention and that many changes and alterations can be made thereof without departing from its spirit and broader aspects.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. A height-adjusting mechanism for a chair or the like comprising:

a base;

a spindle rotatably mounted in said base;

a nut threadably mounted on said spindle;

chair-supporting means operably connected to said nut and being fixed against rotation with respect thereto; detent means slidably mounted on said spindle and fixed against rotation with respect thereto, said detent means engaging said nut for normally holding said nut against rotation with respect thereto, said detent means being disengageable from said nut upon the exertion of a predetermined force; and

means for locking said spindle against rotation with respect to said base whereby rotation of said chairsupporting means with sufficient force to disengage said detent means from said nut causes said nut to thread on said spindle.

2. The height-adjusting mechanism of claim 1 in which said chair-supporting means is carried on said detent means and said detent means rests on said nut.

3. The height-adjusting mechanism of claim 2 in which said detent means comprises a washer having at least one downwardly protruding detent; said nut including at least one depression in the top surface thereof for receiving said detent; said chair support means being slidably joined to said nut whereby said chair-support means can be slid vertically with respect to said nut at least a distance great enough to allow said detent to slide out of said depression.

4. The height-adjusting mechanism of claim 3 in which said chair-support means comprises a column, generally sleeve like in configuration; said column including a collar at the base thereof, said collar resting on said washer and embracing said nut, said collar including an opening therein through which said spindle passes, said collar including a generally vertical, elongated slot; a pin on said nut projecting radially therefrom through said slot.

5. The height-adjusting mechanism of claim 4 in which said washer includes a key projecting radially inwardly; said spindle including a groove therein extending generally from top to bottom thereof; said key being positioned within said groove to thereby fix said washer against rotation with respect to said spindle.

6. The height-adjusting mechanism of claim 3 in which said washer includes a key projecting radially inwardly; said spindle including a groove therein extending generally from top to bottom thereof; said key being positioned within said groove to thereby fix said washer against rotation with respect to said spindle.

7. A height-adjusting mechanism for a chair or the like comprising:

a base;

a spindle rotatably mounted in said base;

a nut threadably mounted on said spindle;

a chair-supporting column operably connected to said nut, being slidable vertically with respect thereto and being fixed against rotation with respect thereto;

a detent washer resting on top of said nut and including at least one downwardly projecting detent;

said nut including at least one detent receiving depression in the top thereof;

said washer being positioned around said spindle and being slidable vertically with respect thereto. but being fixed against rotation with respect thereto; said column resting on said washer;

means for locking said spindle against rotation with respect to said base whereby rotation of said column with sufficient force to disengage said detent from said depression causes said nut to thread on said spindle.

8. The height-adjusting mechanism of claim 7 in which said column includes an elongated, generally vertical slot near the base thereof; said nut including a pin projecting radially therefrom and engaging said slot.

9. The height-adjusting mechanism of claim 8 in which said washer includes a key projecting radially inwardly; said spindle including a groove therein extending generally from top to bottom thereof; said key being positioned within said groove to thereby fix said washer against rotation with respect to said spindle.

10. The height-adjusting mechanism of claim 9 in which said column comprises a sleeve having a collar at the bottom thereof; said collar resting on said washer and embracing said nut; said collar including an opening therethrough through which said spindle passes; said collar including an elongated, generally vertical slot through which said pin passes.

11. The height-adjusting mechanism of claim 7 in which said washer includes a key projecting radially inwardly; said spindle including a groove therein extending generally from top to bottom thereof; said key being positioned within said groove to thereby fix said with respect to said spindle. 

1. A height-adjusting mechanism for a chair or the like comprising: a base; a spindle rotatably mounted in said base; a nut threadably mounted on said spindle; chair-supporting means operably connected to said nut and being fixed against rotation with respect thereto; detent means slidably mounted on said spindle and fixed against rotation with respect thereto, said detent means engaging said nut for normally holding said nut against rotation with respect thereto, said detent means being disengageable from said nut upon the exertion of a predetermined force; and means for locking said spindle against rotation with respect to said base whereby rotation of said chair-supporting means with sufficient force to disengage said detent means from said nut causes said nut to thread on said spindle.
 2. The height-adjusting mechanism of claim 1 in which said chair-supporting means is carried on said detent means and said detent means rests on said nut.
 3. The height-adjusting mechanism of claim 2 in which said detent means comprises a washer having at least one downwardly protruding detent; said nut including at least one depression in the top surface thereof for receiving said detent; said chair support means being slidably joined to said nut whereby said chair-support means can be slid vertically with respect to said nut at least a distance great enough to allow said detent to slide out of said depression.
 4. The height-adjusting mechanism of claim 3 in which said chair-support means comprises a column, generally sleeve like in configuration; said column including a collar at the base thereof, said collar resting on said washer and embracing said nut, said collar including an opening therein through which said spindle passes, said collar including a generally vertical, elongated slot; a pin on said nut projecting radially therefrom through said slot.
 5. The height-adjusting mechanism of claim 4 in which said washer includes a key projecting radially inwardly; said spindle including a groove therein extending generally from top to bottom thereof; said key being positioned within said groove to thereby fix said washer against rotation with respect to said spindle.
 6. The height-adjusting mechanism of claim 3 in which said washer includes a key projecting radially inwardly; said spindle including a groove therein extending generally from top to bottom thereof; said key being positioned within said groove to thereby fix said washer against rotation with respect to said spindle.
 7. A height-adjusting mechanism for a chair or the like comprising: a base; a spindle rotatably mounted in said base; a nut threadably mounted on said spindle; a chair-supporting column operably connected to said nut, being slidable vertically with respect thereto and being fixed against rotation with respect thereto; a detent washer resting on top of said nut and including at least one downwardly projecting detent; said nut including at least one detent receiving depression in the top thereof; said washer being positioned around said spindle and being slidable vertically with respect thereto, but being fixed against rotation with respect thereto; said column resting on said washer; meanS for locking said spindle against rotation with respect to said base whereby rotation of said column with sufficient force to disengage said detent from said depression causes said nut to thread on said spindle.
 8. The height-adjusting mechanism of claim 7 in which said column includes an elongated, generally vertical slot near the base thereof; said nut including a pin projecting radially therefrom and engaging said slot.
 9. The height-adjusting mechanism of claim 8 in which said washer includes a key projecting radially inwardly; said spindle including a groove therein extending generally from top to bottom thereof; said key being positioned within said groove to thereby fix said washer against rotation with respect to said spindle.
 10. The height-adjusting mechanism of claim 9 in which said column comprises a sleeve having a collar at the bottom thereof; said collar resting on said washer and embracing said nut; said collar including an opening therethrough through which said spindle passes; said collar including an elongated, generally vertical slot through which said pin passes.
 11. The height-adjusting mechanism of claim 7 in which said washer includes a key projecting radially inwardly; said spindle including a groove therein extending generally from top to bottom thereof; said key being positioned within said groove to thereby fix said washer against rotation with respect to said spindle. 